A not-so-well-known fact about the 802.11n wireless standard is that if you want to maximize the range and speed of your 802.11n router, the router needs to be set internally to only accept wireless connections from 802.11n wireless adapters (this is usually a setting in the router called N-only mode). If the router is set to allow 802.11g adapters to connect (usually called Mixed N/G/B modes) the performance of the whole network drops. By factory default, most 802.11n routers are going to be set to mixed mode.
With the price of 802.11n equipment dropping, it is not expensive to get 802.11n adapters for all computers in your home. But what happens if you have a device such as the TiVo Series 2 DVR, for which there are no compatible 802.11n USB adapters (at the time of this writing)? Sure you can hardwire the TiVo directly to your router, but if your TiVo is on the other side of the house, that is not a good option.
There are two workarounds you can deploy so that your TiVo can continue to get wireless connectivity without bringing down the performance of your 802.11n network.
Option 1: Use your old G router (or buy a new one) as an access point connected to your N router. You will likely need to search Google or another search engine for your router model number to figure out how to change the router to AP mode (most routers have an AP mode, but some do not). You can then connect the Internet port on your G router to an ethernet port on your N router using a standard ethernet cable, and then broadcast a wireless signal from the G router. This signal is completely separate from your 802.11n signal and will have its own SSID (signal name). You can use this signal to connect your G devices, such as the TiVo, to the Internet. And your 802.11n router can be set to only accept connections from 802.11n devices.
Option 2: The other workaround is to buy a wireless adapter that has an AP mode function, such as the RokAir which is compatible with Macs and Windows, and install it to a computer that will be hardwired to your 802.11n router. Using the AP mode feature of the RokAir, you can share your wired Internet connection wirelessly with other devices. Doing so will create a new wireless signal that is separate from your 802.11n signal, and then you can connect to this new signal with your G devices, like the TiVo. Meanwhile, just as with option 1, your 802.11n router can be set to only accept connections from 802.11n devices. The main difference between this option and option 1 is that you will have to leave the computer that has the AP mode device powered on when you want the TiVo to be able to connect to the Internet. If you turn that computer off, the TiVo will not be able to connect.
You could also wait to see if TiVo introduces an 802.11n wireless device (which would be awesome), but it appears a lot of the new software based features they are adding only work with Series 3/TiVo HD boxes. So there is some speculation that a new 802.11n adapter for TiVos may not be supported on Series 2 boxes.